The present invention relates to gas turbine engine casings, particularly gas turbine engine fan casings, more particularly to an improved blade containment assembly for use within or forming a part of the gas turbine engine casing.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor which is enclosed by a generally cylindrical, or frustoconical, fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
There is a remote possibility that with such engines that part, or all, of a fan blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical, or frustoconical, relatively thick metallic containment rings. It is also known to provide generally cylindrical, or frustoconical, locally thickened, isogrid, metallic containment rings. Furthermore it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
However, in the event that a blade becomes detached, the blade strikes the metal casing and a significant load is imparted from the main impact region of the metal casing to a flanged interface with an intake casing.
It is normal practice to transfer the impact loads along the metal casing to the flanged interface with the intake casing using a stepped increase in diameter of the metal casing, as shown in our published European patent application No. EP0965731A2. The stepped increase in diameter of the metal casing produces a local increase in stresses due to the bending moment at the stepped increase in diameter. The bending moments are counteracted by locally thickening the metal casing at the stepped increase in diameter of the metal casing. The locally thickened stepped increase in diameter adds weight to the metal casing, and the weight may be considerable if the metal casing is for a high bypass ratio turbofan gas turbine engine. The metal casing between the flanged interface with the intake casing and the stepped increase in diameter of the metal casing has a reduced thickness relative to the main impact zone of the metal casing.
Accordingly the present invention seeks to provide a novel gas turbine engine casing which reduces the loads transferred to the flange of the intake casing.
Accordingly the present invention provides a gas turbine engine rotor blade containment assembly comprising a generally cylindrical, or frustoconical, containment casing, the containment casing having a flange for connecting the containment casing to a flange on an axially adjacent casing, the flange on the containment casing having a plurality of circumferentially spaced regions, the regions being removably connectable to the flange on the axially adjacent casing, the ratio of the thickness of the flange of the containment casing to the thickness of a portion of the containment casing adjacent to the flange is between 3 to 1 and 6 to 1, the flange on the containment casing being radially scalloped between the adjacent regions to allow the flange on the fan containment casing to deform such that loads transmitted to the fasteners and flange of the axially adjacent casing are at least reduced.
Preferably the containment casing has an upstream portion and a blade containment portion, the flange is on the upstream portion of the containment casing and the ratio of the thickness of the flange on the upstream portion of the containment casing to the thickness of the upstream portion of the containment casing is between 3 to 1 and 6 to 1.
Preferably the flange on the portion of the containment casing is radially scalloped to the diameter of the outer surface of the portion of the containment casing.
Preferably the containment casing comprises a transition portion, the diameter of the upstream portion being greater than the diameter of blade containment portion, the transition portion connecting the blade containment portion and the upstream portion to transmit loads from the blade containment portion to the upstream flange.
Preferably the transition portion having a smoothly curved increase in diameter between the blade containment portion and the upstream portion whereby the transition region is allowed to flex to reduce impact loads transmitted to the upstream flange.
Preferably the thickness of the transition portion being substantially the same as the thickness of the upstream portion of the containment casing.
The thickness of the transition portion may be between 75% and 125% of the thickness of the upstream portion of the containment casing.
The containment casing may have ribs and/or flanges. One or more continuous layers of a strong fibrous material may be wound around the containment casing.
The containment casing may comprise any suitable metal or metal alloy. Preferably the metal containment casing comprises a steel alloy, aluminium, an aluminium alloy, magnesium, a magnesium alloy, titanium, a titanium alloy, nickel or a nickel alloy.
An acoustic lining may be provided within the containment casing.
The blade containment portion may have a radially inwardly and axially upstream extending flange, the flange being arranged at the upstream end of the blade containment portion.
Preferably the thickness of the blade containment portion is greater than the thickness of the upstream portion.
The containment casing may be a fan containment casing, a compressor containment casing or a turbine containment casing.